Pre-chamber system for an internal combustion engine

ABSTRACT

A pre-chamber system for an internal combustion engine, in particular for a gas engine, comprising a pre-chamber volume in which an ignitable fuel-air mixture can be fired—in particular by an ignition device which can be arranged at the pre-chamber system—, wherein the pre-chamber system is provided with a flow transfer passage by which the pre-chamber volume can be connected to a main combustion chamber of the internal combustion engine, wherein the pre-chamber volume includes an ignition region and a flow transfer region which is at least portion-wise delimited from the ignition region by an intermediate wall, wherein the fuel-air mixture can be fired in the ignition region and the flow transfer passage opens into the flow transfer region and there is provided an air feed passage, wherein—preferably compressed—air can be fed to the flow transfer region by way of the air feed passage.

The present invention concerns a pre-chamber system for an internalcombustion engine as set forth in claim 1 as well as an internalcombustion engine having such a pre-chamber system.

In operation of an internal combustion engine—in particular a gasengine—with a substantially stoichiometric ratio of fuel and air veryhigh temperatures can occur, which is detrimental to the exhaust gasbehavior of such an engine. It is possible to counteract that situationby exhaust gas recycling. That however leads to a worsening in terms ofthe ignition characteristics.

Using a pre-chamber to be filled with combustion gas for ignitionpurposes in that case, as is a standard solution adopted in regard tolarge-volume lean-burn engines, is initially problematic. For themixture which upon compression is urged out of the main combustionchamber into the pre-chamber does not in fact have an air excess,whereby a fuel-air mixture which can be well ignited does not prevail inthe pre-chamber.

In DE 35 06 217 A1 that problem is avoided by a near-stoichiometricallymixed fuel gas already being fed to the pre-chamber. A disadvantage inthat respect, besides the increased structural complication andexpenditure, is that when the injection valve of the pre-chamber suffersfrom wear there is the possibility of back-ignition of the pre-chambermixture into the supply passages. That represents a safety risk whichshould be avoided.

The object of the present invention is to provide a pre-chamber systemwhich even in a stoichiometric mode of operation of a large-volumeengine with substantial exhaust gas recycling allows good ignition ofthe fuel-air mixture in the pre-chamber without at the same timeintroducing a safety risk due to the presence of an ignitable fuel-airmixture outside the combustion chambers.

That object is attained by a pre-chamber system having the features ofclaim 1 and with an internal combustion engine having such a pre-chambersystem.

Dividing the pre-chamber volume into an ignition region and a flowtransfer region which is at least partially separated from the ignitionregion by an intermediate wall and introducing air through the air feedpassage into the flow transfer region provides that a minimum of exhaustgas-bearing combustion mixture passes out of the main combustion chamberinto the ignition region during the compression phase. At the same timethat main chamber gas urges the air introduced through the air feedpassage into the ignition region, thereby affording there a mixturewhich can enjoy good ignition. In that way a lambda value of between 0.8and 1.2 can be achieved in the ignition region of the pre-chamber,wherein the lambda value relates to the ratio of air to fuel and thelambda value of 1 represents the ideal, that is to say stoichiometric,ratio.

DE 10 2008 062 574 A1 discloses a spark plug for an internal combustionengine, which has a post-chamber volume region, wherein thatpost-chamber volume region at least partially surrounds a combustionchamber-side end region of the spark plug. That however only serves toincrease the volume of the pre-chamber and does not attain the presentobject. For, the absence of an intermediate wall does not prevent themixture from passing from the main combustion chamber to the ignitionregion upon compression.

Further advantageous embodiments of the invention are defined in thedependent claims.

To make it easier for the ignition flame produced by ignition in thepre-chamber to reach the main combustion chamber, a connecting passagecan be provided in the intermediate wall, the connecting passageconnecting the ignition region to the flow transfer region.

To achieve uniform cooling of the entire pre-chamber by virtue of theinjected air it can be provided that the intermediate wall is of asubstantially peripherally extending configuration in relation to alongitudinal axis of the pre-chamber system, wherein the flow transferregion substantially surrounds the ignition region—separated by theperipherally extending intermediate wall.

A preferred embodiment is one in which by way of the air feed passagea—preferably cooled—charge air of the internal combustion engine and/ora compressed air—preferably compressed to between 6 bars and 10 bars—canbe introduced into the flow transfer region. That further contributes toeffectively keeping the exhaust gas-bearing mixture away from theignition region.

In that case for energy reasons it can be provided that firstly chargeair which is typically available at a pressure of between 2 and 3 barsfrom a turbocharger is fed and then, as soon as the pressure in thepre-chamber exceeds the pressure of the charge air, compressed air isfed.

For precise control or regulation of the period of time of the air feedor the amount of air which is fed, it can be provided that arranged atthe air feed passage is a valve which is preferably electronic.

For optimum propagation of the fed air it can be provided that aperipherally extending annular passage is provided in the flow transferregion in relation to a longitudinal axis of the pre-chamber system,wherein preferably the air feed passage opens into the annular passage.To permit a rolling-like inflow of the air, in that case a peripherallyextending annular gap can be provided between the annular passage andthe rest of the flow transfer region, wherein considered radially withrespect to the longitudinal axis the annular passage has an annularpassage width and the annular gap has an annular gap width, whereinpreferably the annular gap width is less than the annular passage width.

So that there is a sufficiently large available volume for pressureequalization a flow transfer volume of the flow transfer region can belarger than an ignition volume of the ignition region.

It can be provided that the connecting passage has a connecting passageopening, wherein the connecting passage opening opens into the flowtransfer region. As it is advantageous in terms of fluid mechanics it isparticularly preferably provided that in relation to a longitudinal axisof the pre-chamber starting from the connecting passage opening asub-volume of the flow transfer region, that faces away from theignition region, is smaller than the remaining residual volume of theflow transfer region.

To achieve particularly directed discharge of the flow the ratio of apassage diameter of the flow transfer passage to a passage length of theflow transfer passage can be at a maximum 0.25. Thus it can be providedboth that the flow transfer passage of the pre-chamber system is of aninclinedly extending configuration with respect to the longitudinalaxis, and also the flow transfer passage with its flow transfer passageopening which opens into the flow transfer region is substantiallytangential in relation to an inside wall of the pre-chamber system. As aresult the flow of the fuel-air mixture which flows into the pre-chamberdue to the compression effect faces away from the ignition volume of thepre-chamber.

In order in comparison to guarantee a directed flow of the ignitionflame into the flow transfer passage, it can be provided that theconnecting passage opening—or at least a part of itscross-section—extends in the direction of the flow transfer passageopening.

Further advantages and details of the invention will be apparent fromthe Figures and the related specific description. In that respect FIGS.1 through 4 show sectional views of various configurations ofpre-chamber systems according to the invention.

FIG. 1 firstly shows the pre-chamber volume 4 of the pre-chamber system1, the ignition device 6, the flow transfer passage 5 with its flowtransfer passage opening 16 and a fuel gas passage 7. The flow transferregion 7 is delimited from the ignition region 3 by an intermediate wall9, the two regions being connected by a connecting passage 11 with aconnecting passage opening 15. The flow transfer passage 5 is heretangential relative to the inside wall 17. An annular gap 3 which isformed in an annular configuration around the longitudinal axis X isconnected to the rest of the flow transfer region 2 by way of an annulargap 14. The air feed passage 8 opens into the annular passage 13; theair feed passage 8 permits both the feed of charge air and also the feedof compressed air, the feed of compressed air being regulated by meansof an electronic valve 12.

FIG. 2 shows a pre-chamber system according to the invention in whichthe connecting passage 11 is also inclined with respect to thelongitudinal axis X. In addition there is a second electronic valve 12which regulates the feed of charge air.

FIG. 3 shows an embodiment without a connecting passage 11.

FIG. 4 shows an embodiment which is similar to FIG. 2 but with adifferent geometry of the flow transfer passage 11, in particular theflow transfer passage opening 15.

The present invention is not limited to the foregoing embodiments. Forexample the flow transfer passage can be arranged centrally along thelongitudinal axis. In that respect it may be advantageous for theconnecting passage opening to be arranged to face away from the flowtransfer passage opening. A mixture, for example with a lambda value of0.3, could also be supplied by way of the fuel gas passage 7.

1. A pre-chamber system for an internal combustion engine, in particularfor a gas engine, comprising a pre-chamber volume in which an ignitablefuel-air mixture can be fired—in particular by an ignition device whichcan be arranged at the pre-chamber system—, wherein the pre-chambersystem is provided with a flow transfer passage by which the pre-chambervolume can be connected to a main combustion chamber of the internalcombustion engine, wherein the pre-chamber volume includes an ignitionregion and a flow transfer region which is at least portion-wisedelimited from the ignition region by an intermediate wall, wherein thefuel-air mixture can be fired in the ignition region and the flowtransfer passage opens into the flow transfer region and there isprovided an air feed passage, wherein—preferably compressed—air can befed to the flow transfer region by way of the air feed passage.
 2. Apre-chamber system as set forth in claim 1 wherein provided in theintermediate wall is a connecting passage, the connecting passageconnecting the ignition region to the flow transfer region.
 3. Apre-chamber system as set forth in claim 1, wherein the intermediatewall is of a substantially peripherally extending configuration inrelation to a longitudinal axis of the pre-chamber system, wherein theflow transfer region substantially surrounds the ignitionregion—separated by the peripherally extending intermediate wall.
 4. Apre-chamber system as set forth in claim 1, wherein by way of the airfeed passage a—preferably cooled—charge air of the internal combustionengine and/or a compressed air—preferably compressed to between 6 barsand 10 bars—can be introduced into the flow transfer region.
 5. Apre-chamber system as set forth in claim 1, wherein a preferablyelectronic valve is arranged for controlling or regulating a period oftime of the feed of air and/or the amount of the fed air in the air feedpassage.
 6. A pre-chamber system as set forth in claim 1, wherein aperipherally extending annular passage is provided in the flow transferregion in relation to a longitudinal axis of the pre-chamber system,wherein preferably the air feed passage opens into the annular passage.7. A pre-chamber system as set forth in claim 6, wherein a peripherallyextending annular gap is provided between the annular passage and therest of the flow transfer region, wherein considered radially withrespect to the longitudinal axis the annular passage is of an annularpassage width and the annular gap is of an annular gap width, whereinpreferably the annular gap width is less than the annular passage width.8. A pre-chamber system as set forth in claim 1, wherein a flow transfervolume of the flow transfer region is larger than an ignition volume ofthe ignition region.
 9. A pre-chamber system as set forth in claim 1,wherein the connecting passage has a connecting passage opening, theconnecting passage opening into the flow transfer region.
 10. Apre-chamber system as set forth in claim 9, wherein in relation to alongitudinal axis of the pre-chamber starting from the connectingpassage opening a sub-volume of the flow transfer region, that facesaway from the ignition region, is smaller than the remaining residualvolume of the flow transfer region.
 11. A pre-chamber system as setforth in claim 1, wherein the ratio of a passage diameter of the flowtransfer passage to a passage length of the flow transfer passage is ata maximum 0.25.
 12. A pre-chamber system as set forth in claim 1,wherein the flow transfer passage of the pre-chamber system is of aninclinedly extending configuration with respect to a longitudinal axis.13. A pre-chamber system as set forth in claim 1, wherein the flowtransfer passage has a flow transfer passage opening, the flow transferpassage opening opening into the flow transfer region.
 14. A pre-chambersystem as set forth in claim 13, wherein starting from the flow transferpassage the flow transfer passage opening opens substantiallytangentially in relation to an inside wail of the pre-chamber systeminto the flow transfer region.
 15. A pre-chamber system as set forth inclaim 1, wherein starting from the ignition region the connectingpassage opening faces in the direction of the flow transfer passageopening.
 16. A pre-chamber system as set forth in claim 15, wherein onlya part of a cross-section of the connecting passage opening faces in thedirection of the flow transfer passage opening.
 17. An internalcombustion engine having a pre-chamber system as set forth claim 1.